When light enters a photographic element and strikes a light-sensitive emulsion layer, a portion of that light is reflected back toward the surface of the element. This effect is known as "back-scatter". When the back-scattered light reaches the surface of the element (i.e., the element/air interface), this light can then be reflected back into the element. This effect is known as "halation". The back-reflected light can then expose portions of light-sensitive layers at large lateral distances from the initial point at which the light entered the element, thus leading to losses in sharpness of the image formed in the element. Similar losses in sharpness can also occur when back-scattered light is reflected back into a photographic element by overlying scattering materials such as silver halides.
It is known, as disclosed in U.S. Pat. No. 4,312,941, to incorporate in an upper layer of a photographic element, a filter dye in order to absorb back-scattered light to reduce the amount of light that is back-reflected into the element.
It has also been known to use development inhibitor releasing (DIR) compounds in photographic elements for a variety of purposes. A primary reason for using such compounds is to improve the sharpness of the image formed in the photographic element. By inhibiting development (and consequently, image formation) at the center of an area of exposure, the DIR compounds enhance the edge of the image area, thus improving sharpness. This improvement, however, is unrelated to the amount of back-reflection of light in the element.